Project Summary: The C-terminal domain (CTD) of RNA polymerase II (RNAPII) is an essential component of transcriptional regulation and RNA processing of protein coding genes. A large body of data also implicates the CTD in the transcription and processing of RNAPII-mediated small nuclear RNA (snRNA) genes. However, the identity of the complex(es) that associate with the CTD and mediate the processing of snRNA genes have remained elusive. We describe an RNA polymerase II complex that contains at least twelve novel subunits, termed the Integrator, in addition to core RNAPII subunits. Two of the Integrator subunits display similarities to the subunits of the cleavage and polyadenylation specificity factor (CPSF) complex. We show that Integrator is recruited to the U1 and U2 snRNA genes and mediates their 3'-end processing. The Integrator complex is evolutionarily conserved in metazoans and directly interacts with the C- terminal domain of the RNA polymerase II large subunit. This proposal is focused at elucidating the role of the Integrator, in control of transcription and cellular proliferation. The three Aims are designed to provide a thorough physical and functional characterization of the Integrator complex. Aim1 describes experiments that will begin to define the function of the individual proteins in the complex and details the functional reconstitution of Integrator. Aim2 describes a detailed functional analysis of Integrator in transcriptional regulation of snRNA genes and extend the work to analysis of other non-coding RNA and RNAPII-mediated genes. Aim3 extends the work by analyzing the role of the complex and its individual subunits in oncogenesis and cell cycle regulation. Elucidation of the mechanism through which small nuclear RNAs are transcribed and processed to mature RNAs is of seminal importance in understanding regulation of gene expression and growth control. Aberrant regulation of small nuclear RNA processing could result in defective messenger RNA processing through deregulation of splicesome and may lead to cellular transformation and oncogenesis.